1. Technical Field
The present invention relates generally to the field of wireless telecommunications; and, more particularly, to a method and apparatus for monitoring one or more telecommunications systems with respect to which a wireless device is in an idle mode while the wireless device is in a connected mode with respect to another system.
2. Description of Related Art
Wireless devices, such as mobile phones, often support multiple telecommunications systems, for example, the system standards GSM (Global System for Mobile Communications) and WCDMA (Wideband Code Division Multiple Access). When such a wireless device is in a connected mode with respect to one supported system, the device may have a need to monitor the one or more other supported systems with respect to which it is in an idle mode. For example, a mobile phone that is in a phone call (connected mode) in one system may have a need to monitor other systems in which it is in an idle mode in order to prepare for a hand-over between the connected system and one of the idle systems. In such a situation, the wireless device must be able to access the connected system and the one or more idle systems via an air interface of the wireless device.
With respect to a system in which the wireless device is in a connected mode, the wireless device transmits and receives user data via the air interface; and, using a receiver associated with the system in the connected mode, also acquires information about the environment of the system in the connected mode. With respect to systems in which the wireless device is in an idle mode, the wireless device uses receivers associated with the systems in the idle mode to acquire information about the environment of the systems in the idle mode. In such a situation, a transmitted signal on the air interface from a transmitter associated with the system in the connected mode may block or interfere with receivers of the systems that are in the idle mode unless suitable precautions are taken.
One known approach to overcoming the interference problem recognizes that the system with respect to which the wireless device is in the connected mode may support transmission gaps, e.g., idle frames in GSM or compressed mode in WCDMA. In such approach, the wireless device may use the transmission gaps to monitor the air interface with respect to a system in which the wireless device is in an idle mode without interference.
Another known approach to overcoming the interference problem is to provide the wireless device with a plurality of antennas, one for each supported system, such that each system can be independently accessed via the air interface.
The approach that utilizes transmission gaps requires that the one or more idle systems and the connected system be synchronized. For example, in a dual system GSM/WCDMA device, to monitor the GSM system, it is required to know the time of the WCDMA compressed mode gaps of the WCDMA system This requirement increases the over-all complexity of the wireless device. Also, for some systems, the transmission gaps have an adverse effect on network performance. For example, the compressed mode gaps in WCDMA reduces the capacity of the system, while the idle frames in GSM also impact the system, although to a lesser extent. An additional disadvantage is that each transmission gap offers only a limited time for monitoring, and the transmission gaps are only available at a limited rate as defined by the system.
The approach that utilizes a different antenna for each system supported by a wireless device requires isolation between the antennas in order to eliminate interference via the air interface. Isolation requirements between antennas in a wireless device restrict the mechanical design options of the device since the antennas usually need to be separated as much as possible. Also, in some wireless devices, it is desirable to have all the air interface signals for all the supported systems available in one common radio frequency interface. This is desirable, for example, in cars with an external antenna that allow only one radio frequency interface between the wireless device and the external antenna on the car.
There is, accordingly, a need for a method and apparatus for monitoring one or more systems with respect to which a wireless device is in an idle mode while the wireless device is in a connected mode with respect to another system, and that does not require using transmission gaps and that provides a negligible air interface interference.